Angiopoietin-like protein 3 promotes preservation of stemness during ex vivo expansion of murine hematopoietic stem cells.

Allogeneic hematopoietic stem cell (HSC) transplantations from umbilical cord blood or autologous HSCs for gene therapy purposes are hampered by limited number of stem cells. To test the ability to expand HSCs in vitro prior to transplantation, two growth factor cocktails containing stem cell factor, thrombopoietin, fms-related tyrosine kinase-3 ligand (STF) or stem cell factor, thrombopoietin, insulin-like growth factor-2, fibroblast growth factor-1 (STIF) either with or without the addition of angiopoietin-like protein-3 (Angptl3) were used. Culturing HSCs in STF and STIF media for 7 days expanded long-term repopulating stem cells content in vivo by ∼6-fold and ∼10-fold compared to freshly isolated stem cells. Addition of Angptl3 resulted in increased expansion of these populations by ∼17-fold and ∼32-fold, respectively, and was further supported by enforced expression of Angptl3 in HSCs through lentiviral transduction that also promoted HSC expansion. As expansion of highly purified lineage-negative, Sca-1+, c-Kit+ HSCs was less efficient than less pure lineage-negative HSCs, Angptl3 may have a direct effect on HCS but also an indirect effect on accessory cells that support HSC expansion. No evidence for leukemia or toxicity was found during long-term follow up of mice transplanted with ex vivo expanded HSCs or manipulated HSC populations that expressed Angptl3. We conclude that the cytokine combinations used in this study to expand HSCs ex vivo enhances the engraftment in vivo. This has important implications for allogeneic umbilical cord-blood derived HSC transplantations and autologous HSC applications including gene therapy.

Lentiviral gene therapy of murine hematopoietic stem cells ameliorates the Pompe disease phenotype.

Pompe disease (acid alpha-glucosidase deficiency) is a lysosomal glycogen storage disorder characterized in its most severe early-onset form by rapidly progressive muscle weakness and mortality within the first year of life due to cardiac and respiratory failure. Enzyme replacement therapy prolongs the life of affected infants and supports the condition of older children and adults but entails lifelong treatment and can be counteracted by immune responses to the recombinant enzyme. We have explored the potential of lentiviral vector-mediated expression of human acid alpha-glucosidase in hematopoietic stem cells (HSCs) in a Pompe mouse model. After mild conditioning, transplantation of genetically engineered HSCs resulted in stable chimerism of approximately 35% hematopoietic cells that overexpress acid alpha-glucosidase and in major clearance of glycogen in heart, diaphragm, spleen, and liver. Cardiac remodeling was reversed, and respiratory function, skeletal muscle strength, and motor performance improved. Overexpression of acid alpha-glucosidase did not affect overall hematopoietic cell function and led to immune tolerance as shown by challenge with the human recombinant protein. On the basis of the prominent and sustained therapeutic efficacy without adverse events in mice we conclude that ex vivo HSC gene therapy is a treatment option worthwhile to pursue.

EZH2-dependent chromatin looping controls INK4a and INK4b, but not ARF, during human progenitor cell differentiation and cellular senescence.

BACKGROUND: The INK4b-ARF-INK4a tumour suppressor locus controls the balance between progenitor cell renewal and cancer. In this study, we investigated how higher-order chromatin structure modulates differential expression of the human INK4b-ARF-INK4a locus during progenitor cell differentiation, cellular ageing and senescence of cancer cells. RESULTS: We found that INK4b and INK4a, but not ARF, are upregulated following the differentiation of haematopoietic progenitor cells, in ageing fibroblasts and in senescing malignant rhabdoid tumour cells. To investigate the underlying molecular mechanism we analysed binding of polycomb group (PcG) repressive complexes (PRCs) and the spatial organization of the INK4b-ARF-INK4a locus. In agreement with differential derepression, PcG protein binding across the locus is discontinuous. As we described earlier, PcG repressors bind the INK4a promoter, but not ARF. Here, we identified a second peak of PcG binding that is located approximately 3 kb upstream of the INK4b promoter. During progenitor cell differentiation and ageing, PcG silencer EZH2 attenuates, causing loss of PRC binding and transcriptional activation of INK4b and INK4a. The expression pattern of the locus is reflected by its organization in space. In the repressed state, the PRC-binding regions are in close proximity, while the intervening chromatin harbouring ARF loops out. Down regulation of EZH2 causes release of the approximately 35 kb repressive chromatin loop and induction of both INK4a and INK4b, whereas ARF expression remains unaltered. CONCLUSION: PcG silencers bind and coordinately regulate INK4b and INK4a, but not ARF, during a variety of physiological processes. Developmentally regulated EZH2 levels are one of the factors that can determine the higher order chromatin structure and expression pattern of the INK4b-ARF-INK4a locus, coupling human progenitor cell differentiation to proliferation control. Our results revealed a chromatin looping mechanism of long-range control and argue against models involving homogeneous spreading of PcG silencers across the INK4b-ARF-INK4a locus.